Drive anywhere in the Cuban countryside and you will spot the marabu lining the road: a dense, woody weed that grows as tall as trees and has invaded vast swathes of agricultural land.

The land-grab began in the 1990s when Cuba was in economic crisis following the collapse of its great benefactor, the Soviet Union. The mighty sugar industry slumped too, and cane fields were overrun by marabu.

But to one British firm, the aggressive weed is less a problem than a valuable resource.